The present invention relates generally to electrical devices having wound coils for excitation thereof, and, more particularly, to methods of making fractional horsepower electric motors.
One of the less expensive types of electric motors are conventionally referred to as "skeleton" or "C-type" motors. These motors typically are of small horsepower and conventionally are provided with a generally U-shaped or C-shaped yoke section which has a rotor receiving bore in the bight portion of the yoke. A core section, adapted for accommodating a wound coil or excitation winding thereon, is provided to bridge the leg portions of the yoke so as to complete a magnetic circuit for the stator. One particular construction that has been used extensively by applicant's assignee is shown and described in Tupper's U.S. Pat. No. 3,024,377 which issued Mar. 6, 1962, and which is assigned to the assignee of the present application.
As pointed out in the just-referenced Tupper patent, it is important that the coil supporting core section (winding leg) be rigidly maintained in fixed relation to the yoke leg portions so as to avoid the introduction of more than a minimum of interference or magnetic reluctance into the flux path along the interfaces of the winding leg and adjacent leg portions of the yoke. The type of winding leg laminations shown and described in the Tupper patent has become known in the industry as a "dog-bone" lamination. This type of lamination is provided with an elongate winding portion and two enlarged ends. Elongate portions having enlarged ends are also shown in the Naul U.S. Pat. No. 2,807,735, which issued Sept. 24, 1957.
With both of the approaches just mentioned, winding leg laminations may be produced from a strip of material substantially at the same time that yoke section laminations are produced; with the different laminations being punched from the strip in a nested relationship. With the Tupper approach, relative small amounts of scrap are produced because of this nested relationship.
Over the years, there has arisen a need to increase the power delivery capability of many of the existing skeleton motor designs. The demand for and expected production volumes for such increased capability motors, in many cases, have not justified the expenses of providing a completely redesigned motor and associated tooling. Thus, for many designs (including those of Tupper) such demand has been met by producing motors of increased stack heights or lengths.
In more recent years, it has become desirable to increase the number of winding turns, or to use aluminum windings rather than copper windings. Use of aluminum has become increasingly important with increasing material shortages, and with increasing differentials between prices of copper and aluminum. In either case, more "winding window" space is usually required, i.e., the space or "window" between the winding leg and bight portions of the stator yoke.
One of the present practices for providing larger winding windows for dog-bone skeleton motors is to discard the dog-bone winding leg laminations that are punched in nested relation with the yoke section; and punch separate winding leg laminations that will provide a larger winding window.
Another alternative to the one just mentioned would be to provide two different complete core designs, one of which would be used when "small windows" were needed, and the other when "large" winding windows were needed. However, this approach would require an initial tooling expense or investment for each design as well as maintenance and replacement expenses for such tooling.
It might be suggested that a more desirable approach would be to redesign existing motor laminations so that a single, larger winding window would always be provided, and then use such redesign even for applications that needed smaller winding windows. This approach would cause other problems however because the overall size of the resulting motors (including windings) would often be larger than motors in the field, and the physical interchangeability of replacement motors might not be possible. Moreover, because of the somewhat greater overall physical size of such motors, it would be necessary (in at least some instances) for appliance manufacturers to modify their products design in order to accommodate the larger motor. This of course would be contrary to the trend toward reduced product sizes.
Accordingly, it would be extremely desirable to provide new and improved motors and methods of making the same, whereby such motors: could be utilized as a direct replacement for small motors that were manufactured heretofore; would have an overall physical configuration that would fit within existing designs of appliances and other devices; and yet in which large winding windows could be provided without the need to scrap substantial amounts of lamination material, and to use in lieu thereof specially made winding leg laminations.